base-files: fix telnet login on musl

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

SVN-Revision: 43006

package/base-files/files/bin/login.sh

@@ -1,8 +1,8 @@
 #!/bin/sh
 # Copyright (C) 2006-2011 OpenWrt.org
 
-if ( ! grep -qs '^root:[!x]\?:' /etc/shadow || \
-     ! grep -qs '^root:[!x]\?:' /etc/passwd ) && \
+if ( ! grep -qsE '^root:[!x]?:' /etc/shadow || \
+     ! grep -qsE '^root:[!x]?:' /etc/passwd ) && \
    [ -z "$FAILSAFE" ]
 then
 	echo "Login failed."